Endangered Northern Right Whales are struck by passing ships while sleeping (and breathing at the sea surface) at an alarming rate. The collisions frequently severely injure or kill the whales. The Northern Right whales are magnificent marine mammals that are large, rotund, black whales with large heads, long rostrums, and no dorsal fins. They can grow up to 53 feet (16.2 meters) long and weigh up to 70 tons. These Northern Right whale, prime target of commercial whaling in previous centuries, had to be placed on the endangered species list. Its population has been reduced in the Atlantic Ocean near the North American continent to about 300 and is still decreasing, now through ship strikes and fishing gear entanglement. Given this, every effort is being taken to protect these whales and give the still declining population a chance to stabilize and grow, and the systems and methods described herein will help to do this.
The Right Whales sleep (and breathe) while drifting at the sea surface and not infrequently get hit by passing ships which often inflict severe injuries or death. These collisions seem to indicate that the often considerable underwater noise generated by approaching vessels is unable to wake up sleeping right whales and entice them to get out of the path of the approaching ships. While awake the whales communicate actively with each other underwater with low frequency moaning sound bursts. To be able to listen from shore to the right whales' vocalization from adequately distributed underwater listening devices would allow researchers and observers to approximately know where the animals are located. Transiting vessels could be warned to change their course, lower their speed, and look out for whales resting in their paths to avoid collisions. Accordingly, it would be useful for researchers to conduct full-time monitoring of natural and man-made underwater noise with oceanographic buoy moorings
Underwater sounds are typically received by an underwater listening device such as a hydrophone, which is typically installed as part of the mooring of an oceanographic surface buoy. The listening device is hard wired to a surface buoy, which transmits the noise to shore based researchers and observers. However, such transmission was only possible at calm sea state conditions and thereby limited to short-time observations. Most of the time wind generated waves are present at the sea surface, causing the surface buoy to follow the wave contours and thereby to raise and lower its mooring connection to the anchor. The vertical mooring motions generate flow noise around any object assembled as part of the buoy mooring. This flow noise masks underwater sound signals of interest and thereby hinders or greatly reduces their effective detection.
In buoy moorings the underwater listening devices (hydrophones) are installed inside of an open cage, with the cage being part of the buoy's mooring connection to its anchor on the sea floor. All offshore buoy moorings need to allow significant vertical and horizontal motions of the surface buoy, since the buoys are designed with sufficient buoyancy to follow the contours of the ocean waves which can be 30 ft or higher in storms depending on location. The wave generated buoy (or ship) motions are known as heave and surge (vertical and horizontal motions respectively). A sensor, for instance a hydrophone with its surrounding cage, connected to the surface buoy with a taut mooring cable will be rapidly lifted, lowered, and simultaneously more slowly oscillated sideways due to the constantly changing position of the contour of the passing by ocean waves, which the buoy is forced to follow. In particular the heave and drop motion can be quite rapid, reaching speeds of 1 to 1.5 meters/second (3 to 5 ft/second). When the hydrophone and its support cage are moved that rapidly through the water, a significant flow noise is generated around the hydrophone and its housing. This flow noise masks the environmental and man-made noises (including whale communications) in an area. In some situations, the hydrophone will only receiving and transmitting irregular water flow noise developed immediately adjacent to the sensor, which is stronger than the more distant whale vocalization and other sounds, unless there is a calm sea state and the sound sensor is near motionless in the water column.
Accordingly, there is a need for a system for reliably and continuously measuring underwater sounds independently of the prevailing sea state.